Due to security concerns, a public security organ or another department may intercept communication content of a user within a legally authorized scope, and such interception is called “lawful interception”. Currently, when a user performs communication by means of a mobile communications network and the like, data such as a voice of the user is carried by the network. For example, after a user A and a user B set up a call, a voice of the user A is sent to a base station where the user A is located, the base station of the user A sends the voice of the user A to a PGW (Packet Data Network Gateway, packet data network gateway) and an SGW (Serving Gate Way, serving gateway), the PGW and the SGW forward the voice of the user A to a base station where the user B is located, and the base station where the user B is located sends the voice of the user A to the user B, to implement transmission of the voice of the user A to the user B; the transmission of a voice of the user B to the user A is similar. Because the data such as the voice of the user is carried by the network, when the data such as the voice of the user needs to be intercepted in the prior art, the data such as the voice of the user is directly obtained from the SGW or the PGW, thereby implementing interception on the user. However, with the development of a mobile communications technology, an idea of position-based D2D (device to device) is being discussed and has brought about some applications. The core of the D2D idea is that data between users can be directly transmitted without being carried by a network if the distance between the users is short enough.